1. Field of the Invention
The invention is related to a hydraulic control system for controlling the operation of a variable camshaft timing (VCT) system. More specifically, the present invention relates to a control system utilized to lock and unlock a lock pin in a VCT phaser.
2. Description of Related Art
Internal combustion engines have employed various mechanisms to vary the angle between the camshaft and the crankshaft for improved engine performance or reduced emissions. The majority of these variable camshaft timing (VCT) mechanisms use one or more xe2x80x9cvane phasersxe2x80x9d on the engine camshaft (or camshafts, in a multiple-camshaft engine). In most cases, the phasers have a rotor with one or more vanes, mounted to the end of the camshaft, surrounded by a housing with the vane chambers into which the vanes fit. It is possible to have the vanes mounted to the rotor, and the chambers in the housing, as well. The housing""s outer circumference forms the sprocket, pulley or gear accepting drive force through a chain, belt or gears, usually from the camshaft, or possibly from another camshaft in a multiple-cam engine. The flow of control fluid (usually engine oil) to and from the vane chambers is controlled by a spool valve.
The VCT system also includes a differential pressure control system (DPCS) for controlling the position of the spool valve. The DPCS utilizes hydraulic force on both ends of the spool. Hydraulic force present on the first end is directly applied hydraulic fluid from the engine oil gallery at full hydraulic pressure. The hydraulic force present on the second end of the spool, which is larger than the first end, is system hydraulic fluid at a reduced pressure from a pulse width modulated (PWM) solenoid or valve.
The second end of the spool is a hydraulic force multiplierxe2x80x94a piston whose cross-sectional area is exactly double the cross-sectional area of the first end of the spool, which is acted on directly by system hydraulic pressure. In this way, the hydraulic forces acting on the spool will be exactly in balance when the hydraulic pressure within the force multiplier is exactly equal to one-half that of system hydraulic pressure. This condition is achievable with a pulse width modulated (PWM) solenoid or valve duty cycle of 50%. The duty cycle of 50% is desirable because it permits equal increases and decreases in force at the force multiplier end of the spool to move the spool in one direction or the other by the same amount. Because the force at each of the opposed ends of the spool is hydraulic in origin, and is based on the same hydraulic fluid, changes in pressure or viscosity of the hydraulic fluid will be self-negating and will not affect the centered or null position of the spool.
The rate in which the spool is moved may be varied by increasing or decreasing the duty cycle of the PWM solenoid or valve. U.S. Pat. No. 5,172,659 is hereby incorporated by reference. Furthermore, it is desirable to fix the angular relationship of the phaser when insufficient fluid pressure is present. By way of example, if insufficient fluid pressure is present, the hydraulic fluid flow for sustaining the vane positions is not capable of maintaining the positions, thereby undesirable vibrations may occur. In order to reduce or eliminate the undesirable vibrations, the angular position of the phaser needs to be maintained using means other than the low fluid pressure. Therefore, it is desirable to have a device and method for using a single source such as the PWM solenoid or valve to achieve both the control of the vane position, and when the vane position cannot be maintained, lock the phaser and hence the vane in a suitably fixed position.
A VCT phaser control system having a locking pin controlled by DPCS control pressure is provided.
A variable cam timing system is provided which comprises a VCT locking pin in hydraulic communication with the control circuit of the differential pressure control system (DPCS).
A variable cam timing system is provided which comprises a VCT locking pin in hydraulic communication with the control circuit of the differential pressure control system (DPCS). Whereby the hydraulic fluid used for controlling the DPCS is also used for operating the VCT locking pin.
A variable cam timing system comprising a VCT locking pin in hydraulic communication with the control circuit of the differential pressure control system (DPCS) is provided. When the control pressure is less than 50% duty cycle the same control signal commands the locking pin to engage and the VCT to move toward the mechanical stop. When the control pressure is greater than 50% duty cycle the locking pin disengages and the VCT moves away from the mechanical stop.
Accordingly, a variable cam timing (VCT) phaser control system for a phaser is provided, which includes: a spool valve disposed to be spring loaded to a null position from fluid pressures at a first end and a second end, the first end being subject to a control fluid and the second end having an area being subject to source fluid; a piston engaging a first end of the spool valve, the piston having an opposite side having a area substantially greater than the area of the second end being subject to source fluid; a locking pin locking the phaser at a fixed angular position, thereby controlling the locking pin free of addition control means; and a controller in fluid communication with both the piston and the locking pin for controlling the control fluid characteristics.